The present invention relates to a system for internal fixation of a bone, and especially for the fixation of fractures of the bone.
For any bone fracture, the orthopaedic specialist must first reduce the fracture and then adequately stabilize and fix the bone to maintain the reduction as the bone heals. Each of these steps is complicated when the bone has suffered multiple fractures or a fracture that is not simply transverse. Fractures of this type usually require some form of internal fixation to reduce and maintain the bone fragments. One conventional approach to reducing bone fragments is with a bone plate extending over a portion of the bone at the fracture site. In one surgical approach, an orthopaedic surgeon may use a specialized clamp applied across the bone while attaching the fixation plate to the bone by screwing a plurality of screw fasteners through holes in the plate into the underlying bone.
Generally, screw fasteners are effective in holding the bone plate tightly against the healthy bone so that fracture may heal properly. However, in less healthy (e.g., osteopenic) bone, the screw threads may not find adequate purchase in the bone to hold the bone and plate together in proper alignment. This may result in non-union of the fracture that may require more invasive revision surgery to correct.
Another problem associated with screw fasteners is occasional breakage of the screw near the plate-bone interface due to stress concentrations arising from poor load sharing among all of the screws and/or high cyclic loading.
A further drawback of the screw fastener approach to internal fixation is that a large variety of screw sizes must be made available for each surgical procedure in order to accommodate variations in patient anatomy and fracture type. Maintaining a large inventory of screw sizes, along with the appropriately sized drills, guides, drivers and fixtures, can be costly. There is also the chance that an inappropriately sized screw may be selected during a procedure.
Fixation approaches have been developed that do not rely upon screw fasteners. For example, cerclage systems utilize one or more cables tightened around a bone to hold the fracture fragments together. The cable construct may include a plate that helps anchor the cables. However, cerclage systems require access around the entire periphery of the bone so it is necessary for the surgeon to dissect soft tissues surrounding the bone. Another problem is that the cerclage cable can exert significant line pressure against the periosteum, which may injure the bone and inhibit healing.
Accordingly, there is a need for a fracture fixation system that provides a stable construct in osteopenic bone and that may be adapted for minimally invasive surgical procedures. There is also a need for a fracture fixation system that reduces the inventory of fasteners and associated instrumentation required during the surgical procedure. There is a further need for a fracture fixation system that assists in improving and maintaining the fracture reduction during application and that incorporates fasteners that resist breakage after implantation and that are less technique sensitive to apply than conventional bone screws.